In the LTE-A (Long Term Evolution-Advanced) Rel-10 (Release-10), only intra-band CA (Carrier Aggregation) is supported in the uplink, and transmission characteristics of radio signals on respective carriers are similar, so uplink transmission timings of the respective carriers are adjusted based on a TA (Time Advance) obtained in the RA (Random Access) procedure on the PCC (Primary Component Carrier), that is, the uplink transmission timings of multiple carriers are aligned, so that such a situation will not occur that an uplink signal in a current uplink sub-frame overlaps in transmission with an uplink signal in an adjacent uplink sub-frame. Since the same TA is used for all the uplink carriers in the uplink sub-frames, uplink out-of-synchronization of the PCC will cause uplink out-of-synchronization of other carriers, and at this time a UE (User Equipment) will obtain a new TA in the RA procedure on the PCC. In this procedure, a PUCCH (Physical Uplink Control Channel), a PUSCH (Physical Uplink Shared Channel), an SRS (Sounding Reference Signal) and other uplink signals will not be transmitted, so a PRACH (Physical Random Access Channel) will not be transmitted concurrently with the PUCCH, the PUSCH, the SRS or other uplink signals.
The PRACH is used to carry a random access preamble sequence so as to obtain the TA value, and as illustrated in FIG. 1, the preamble sequence is consisted of a CP (Cyclic Prefix) and a sequence, where the length of the CP is TCP, and the length of the sequence is TSEQ. A GT (Guard Time) is reserved at the end of the PRACH, and the structure of the PRACH is as illustrated in FIG. 2, where the length of the PRACH is the duration of one TTI (Transmission Time Interval). The CP and the GT are used to avoid interference between the PRACH and a previous or succeeding uplink sub-frame, and the values of the CP and the GT reflect the maximal RTD (Round Trip Delay) decided by the cell size and the maximal channel delay spread.
In order to support coverage of different cells, five preamble formats are defined in the LTE system, and their particular parameters are as depicted in Table 1.
TABLE 1Number K ofsub-framesoccupiedPreamble formatTCPTSEQby PRACH0 (normal format) for a3168 · TS24576 · TS1cell radius ofapproximately 15 km1 (a long CP) for a cell21024 · TS 24576 · TS2radius of approximately 30to 100 km (exclusive)2 (a short CP and a6240 · TS2 · 24576 · TS2repeated preamblesequence) for a cell radiusof approximately 30 km3 (a long CP and a21024 · TS 2 · 24576 · TS3repeated preamblesequence) for a cell radiusof approximately 100 km4 (only applicable to a 448 · TS4096 · TSTDD specialTDD system) for a hotspotsub-framesareaUpPTS
Ts represents a system sample interval of a carrier on which the preamble sequence is transmitted, where Ts=1/30720 ms (millisecond). The format 4 is specific to the TDD (Time Division Duplexing) system and is used for a hotspot area with the radius of approximately 2 kilometers and transmitted only in an UpPTS (Uplink Pilot Time Slot) configured with two SC-FDMA (Single Carrier-Frequency Division Multiple Access) symbols starting at 4832 Ts ahead of the end of an UpPTS sub-frame. The configuration of each carrier is decided by the higher layer. The PRACH with the transmission length of more than 1 ms typically occupies the consecutive uplink sub-frames for transmission.
In the LTE-A Rel-10, target transmit power PPUCCH(i) of the PUCCH transmitted on the PCC in an uplink sub-frame i, target transmit power PPRACH(i) of the PRACH transmitted on the PCC, target transmit power PPUSCH,c(i) of the PUSCH transmitted on each carrier and target transmit power PSRS,c(i) of the SRS transmitted on each carrier are defined for a CA UE, where c represents the carrier index, and i represents the sub-frame.
In the LTE-A Rel-10, concurrent transmission of the PUCCH and the PUSCH on the same carrier or different carriers is supported in the same uplink sub-frame, and concurrent transmission of the PUSCHs on different carriers is supported in the same uplink sub-frame. If the total transmit power of the UE in the current uplink sub-frame i would exceed the allowed maximum transmit power of the UE, then transmit power of the uplink signals in the uplink sub-frame need to be scaled by the same scaling factor according to the priorities of the uplink signals, that is, the uplink transmit power of the UE is controlled in such a way that the same power scaling factor applies to uplink signals with the same priority of the uplink signals. During the power scaling, the UE preferentially ensures not to scale down the target transmit power of the PUCCH, and firstly scales down the target transmit power of the PUSCH on each carrier c, so that the sum of the transmit power of all the uplink signals after power scaling does not exceed the allowed maximum transmit power PCMAX(i) of the UE, that is:
            Σ      c        ⁢                  w        ⁡                  (          i          )                    ·                                    P            ^                                PUSCH            ,            c                          ⁡                  (          i          )                      ≤      (                                        P            ^                    CMAX                ⁡                  (          i          )                    -                                    P            ^                    PUCCH                ⁡                  (          i          )                      )  
{circumflex over (P)}PUSCH,c(i) represents a linear-domain value of PPUSCH,c(i), {circumflex over (P)}PUCCH(i) represents a linear-domain value of PPUCCH(i), {circumflex over (P)}CMAX (i) represents a linear-domain value of {circumflex over (P)}CMAX(i), and w(i) represents a power scaling factor for the carrier c where 0≦w(i)≦1. If no PUCCH is transmitted in the current uplink sub-frame i, then {circumflex over (P)}PUCCH,c(i)=0. Moreover when the UE performs uplink power control, the power scaling factor w(i) can be determined firstly if the target transmit power of the PUSCHs needs to be scaled down, and preferably the determined power scaling factor w(i) meets the following condition: the sum of the transmit power of all the uplink signals does not exceed the allowed maximum transmit power PCMAX(i) of the UE after the target transmit power of the PUSCHs are scaled down. Then the UE scales down the target transmit power of the PUSCHs according to the determined w(i).
If the PUSCHs of the UE in the current uplink sub-frame i include a PUSCH with UCI (Uplink Control Information) and PUSCH(s) without UCI and the total transmit power of the UE would exceed the allowed maximum transmit power of the UE, then the UE preferentially ensures not to scale down the target transmit power of the PUSCH with UCI, and scales down the target transmit power of the PUSCH(s) without UCI on each carrier by the same scaling factor, so that the sum of the transmit power of all the uplink signals after power scaling does not exceed the allowed maximum transmit power of the UE, that is:
                              P          ^                          PUSCH          ,          j                    ⁡              (        i        )              =          min      ⁡              (                                                            P                ^                                            PUSCH                ,                j                                      ⁡                          (              i              )                                ,                      (                                                                                P                    ^                                    CMAX                                ⁡                                  (                  i                  )                                            -                                                                    P                    ^                                    PUCCH                                ⁡                                  (                  i                  )                                                      )                          )                                Σ                  c          ≠          j                    ⁢                        w          ⁡                      (            i            )                          ·                                            P              ^                                      PUSCH              ,              c                                ⁡                      (            i            )                                ≤          (                                                  P              ^                        CMAX                    ⁡                      (            i            )                          -                                            P              ^                        PUCCH                    ⁡                      (            i            )                          -                                            P              ^                                      PUSCH              ,              j                                ⁡                      (            i            )                              )      
If the total transmit power of the UE still would exceed the allowed maximum transmit power of the UE when the transmit power of all the PUSCHs without UCI is scaled down to zero, then the transmit power of the PUSCH with UCI can be further scaled down.
In the LTE-A Rel-11, CA across different frequency bands in the uplink and a hybrid CA deployment of a macro base station and an RRH (Remote Radio Head) can be supported. Since transmission characteristics and transmission paths of radio signals in the different frequency bands may be different, there may be different uplink transmission delays so that signals on different carriers transmitted in the same uplink sub-frame may arrive at the base station at different times. Therefore the uplink transmission timing of the different carriers may be adjusted by using different TAs in the Rel-11. In view of this, the concept of a TA group has been introduced to the LTE-A Rel-11, where carriers with the same or similar transmission delays are considered as one group and referred to as a TA group, the same TA applies to carriers in the same TA group, and a TA value corresponding to the TA group is obtained in the RA procedure on one of carriers in the TA group. When uplink out-of-synchronization of a TA group occurs, the uplink synchronization will be achieved by the RA procedure on a predetermined carrier in the TA group. For a TA group including the PCC, the PCC is the carrier on which the RA procedure is performed, and for a TA group including only SCCs (Secondary Component Carriers), one of the SCCs can be selected for the RA procedure, so the PRACH transmission on an SCC is supported in the LTE-A Rel-11, and at present it is determined that concurrent transmission of PRACHs on multiple carriers in an uplink sub-frame is not supported.
When a PRACH is transmitted on an SCC in a TA group in uplink out-of-synchronization, a PUCCH/PUSCH or another uplink signal may be transmitted on one or more uplink carriers in another TA group in uplink synchronization, so concurrent transmission of the PRACH and the PUCCH/PUSCH needs to be supported in the LTE-A Rel-11. In view of misalignment of uplink transmission timing of the PRACH and the PUCCH/PUSCH in the same uplink sub-frame and possible continuous transmission of the PRACH (e.g., in the preamble formats 1, 2 and 3) across multiple uplink sub-frames, the PUCCH/PUSCH in the uplink sub-frame where it is located may overlap in transmission with the PRACH in all or a part of SC-FDMA symbols. At present there is no particular solution of performing uplink power control in the case that the PRACH overlaps in transmission with the PUCCH/PUSCH to ensure the total transmit power of the respective uplink signals not to exceed the allowed maximum transmit power of the UE in the prior art.